1. Field of the Invention
This invention relates to the recovery of petroleum from a subterranean formation and more particularly pertains to a new and improved process for heating a petroleum-bearing formation by injecting thermal energy therein for recovering the heavy viscous petroleum therefrom.
2. Description of the Prior Art
Through the years many processes have been developed for recovering heavy viscous petroleum from petroleum-bearing formations to reduce the petroleum viscosity by elevating its temperature. As known, viscosity reduction increases the mobility of the petroleum through the formation thereby enabling it to be withdrawn by conventional techniques such as natural flow, pumping, etc. Such thermal introduction processes have employed thermal energy in a wide variety of forms, such as hot water, in-situ combustion, steam, heated condensable and non-condensable gases, and the like. However, steam, either alone or in combination with other thermal energy agents, has been the most widely employed for it has been found to be the most efficient and economical.
Generally speaking, there are two basic processes or techniques for introducing steam into a formation for increasing the recovery of heavy viscous petroleum. One technique is usually referred to as "steam drive" or the like wherein steam is injected into a formation by means of an injection well. The injected steam heats the formation and viscous petroleum and drives the heated petroleum toward one or more adjacent producing wells which are employed to withdraw it to the surface. The second basic technique is commonly referred to as "single well injection," "huff-and-puff" or the like wherein the steam is injected into a formation through a single injection well in a predetermined quantity (huff phase), the formation is allowed to "soak" during which the heat permiates, heating a larger volume of the reservoir, and the heated, mobile petroleum is then produced or withdrawn from the formation through the same well (huff phase).
There are, of course, many modified versions of these basic steam injection techniques known in the art. Many of such processes include the injection of other materials along with or alternately with steam into the formation. By way of example, see U.S. Pat. Nos. 3,292,702; 3,409,083; 3,500,931, and 3,782,470 which disclose modified versions of the above "huff-and-puff" single well steam injection technique.
Many of the known steam injection techniques have been useful in the recovery of certain types of crudes under certain conditions. However, there are several formations known to contain heavy viscous petroleum from which the petroleum has not been recovered in any great quantities by the employment of any known process, including the steam injection processes. These formations are saturated with heavy viscous petroleum usually having API gravities of below about 22.degree. (at 60.degree.F.) and viscosities greater than about 200 centipoise (at 60.degree.F.). Further, many of these formations have low relative permeabilities to oil and water such that they will not accept the direct injection of heated fluids containing steam at sufficiently high injection rates to permit economic recovery of the heavy viscous petroleum. Specific examples of such low relative permeability formations containing such heavy viscous crudes include Pennsylvanian sandstones, such as the Bartlesville sandstone, of the Cherokee group, located in southern Illinois, western Missouri, southeastern Kansas and eastern Oklahoma. Previous attempts to recover such heavy viscous crudes from such formations having low relative permeabilities to water and oil by the employment of known steam injection techniques have heretofore proven unsuccessful inasmuch as such techniques have been incapable of introducing sufficient heat into the formations to permit the recovery of sufficient quantities of the petroleum for economical operation.
Accordingly, it is a principal object of the present invention to provide a process for the recovery of heavy viscous petroleum, particularly crudes having API gravities of below about 22.degree. (at 60.degree.F.), and viscosities greater than about 200 centipoise (60.degree.F.), from formations having low relative pemeabilities to oil and water.
It is another object of the present invention to provide a process for injecting sufficient quantities of heat into such formations having low relative permeabilities to oil and water to permit economic recovery of such heavy viscous crudes contained therein.
It is yet another object of the present invention to provide a process for injecting a heated fluid containing steam into a petroleum-bearing formation having low relative permeabilities to oil and water, in sufficient quantities and at high injection rate, to permit the recovery of heavy viscous crudes therefrom efficiently and economically.
It is yet another object of the present invention to provide a new and improved single well steam injection process for the recovery of such heavy viscous petroleum from such formations having low relative permeabilities to oil and water.
Other objects and advantages of the present invention will become readily apparent to those having ordinary skill in the art from reading this specification and claims in detail.